Pesi (Nyahururu) Dam is located in Nyandarua County on Pesi River and about 1.5km upstream of the confluence of Pesi and Gathanji Rivers. It is located 37km to the south-west of Nyahururu Town. The name of the dam as originally proposed in the National Water Master Plan of 1992 and as indicated in Kenya Government vision 2030 development plan is Nyahururu Dam. The dam was proposed to supply water to Nyahururu Town and its environs.
The original Nyahururu Dam site was proposed about 4km to the west of Nyahururu Town and in Laikipa County. On assessment of the suitability of the site for development of a large dam to supply Nyahururu Town with water in year 2015.
The site was found not to be suitable due to environmental changes that have taken place since 1992. These changes include high level of water pollution due to human settlement in the dam catchment area that include establishment of housing estates like Kia Maina settlement and Coresite estates, cultivated catchment that require rehabilitation and permanent structures that would be affected that include a section of Nyahururu -Nakuru Road.
Besides environmental changes, the proposed original dam site would require water to be pumped to the water supply area: The top water level in the proposed dam is at contour 2400masl while the existing storage tank for supply of water to Nyahururu and its environs is at contour 2400masl which means that the dam could not supply water by gravity.
Pumping of water could raise maintenance and operations cost of the water system to unsustainable level like the existing water system that is currently serving Nyahururu Town. Therefore, an alternative dam site was explored and found on Pesi River hence the name Pesi (Nyahururu) Dam.
The primary objective of Pesi (Nyahururu) Dam Water Supply Project is to provide reliable and sustainable domestic water supply to Nyahururu Town and environs, Ol Kalou Town and environs and other needy areas that can be supplied with water by gravity from the dam.
The secondary objective of Pesi (Nyahururu) Dam Water Supply Project is to provide water for irrigation, hydropower generation and scenery for tourism and sporting activities.
Proposed dam capacity
The proposed Pesi (Nyahururu) Dam will be 60m high and will impound a total of 16,000,000m3 of water. Dam capacity required to meet the projected water demand is 11,300,000m3. The dam crest will be 380m long. The bottom water outlet after water treatment will be at contour 2460masl which will be high enough to command gravity flow to most of the supply target areas.
(ii) Type of Dam and Construction Materials
The proposed dam will be an earth-fill dam. The soils at the dam site and in the vicinity of the dam are red soils that have high cohesion values with low permeability. The soils are non-dispersive. The soils are good for dam construction.
Other construction materials like ballast can be obtained by crushing hard-stone which is readily available within reasonable haulage distance from the dam site.
(iii) Benefits to persons in the vicinity of the proposed dam
Besides getting employment during construction of the project, the water supply that is currently serving the people and which does not cover 25% of the target area will be expanded to serve all the people around the dam area.
Areas to be served with water
The proposed Pesi (Nyahururu) Dam will supply water to areas of Nyandarua and Laikipia Counties. The areas to be served in Laikipia County include Nyahururu, Marmanet and Wiyumiririe Towns and their environs. The areas of Nyandarua County that will be served with water include Ndaragwa, Gwa Kung’u, Mairo-Inya, Ol Joro Orok, Kasuku, Part of Rurii and Ol Kalou Towns and environs that include several sub-locations/locations.
The populations and total water demands are estimated as follows:
Present Year 2015
Initial Year 2019
Future Year 2029
Ultimate Year 2039
Nyahururu-Ol Kalou (Manguo- Nyahururu & Manguo-Ol Kalou Branch lines)
Nyahururu, Marmanet, Gatimu,
Ol Joro Orok, Ol Kalou
Wiyumiririe & Environs
Leshau, Kiriita, Mathingira Locations